The semiconductor device manufacturing industry has changed dramatically since its inception some twenty-five years ago. The minimum feature size of circuits on chips and transistors per bit decreased as productivity increased. Such changes necessitated and drove the search for new more efficient manufacturing processes.
One dynamic area for change in manufacturing processes of semiconductor products has been in fabrication automation. The motivations for automation are clear, viz., product cost minimization, shortened production cycles and improved product quality. One of the prime factors affecting the foregoing is the interaction of people with the manufacturing processes. Generally stated, to the extent work can be physically isolated from the workers, the objectives of wafer fabrication automation can be met. The effects of human error and contamination are fast becoming intolerable in the wafer fabrication process.
One area of the wafer fabrication process in which automation can be applied is the movement of wafer cassettes. Wafer cassettes are holders for silicon wafers in which, usually, the wafers are arranged vertically on shelves. Hitherto, such wafer cassettes, or simply cassettes, had to be moved by a worker from one work station to another. Such movements are subject to human clumsiness, whereby cassettes can be dropped or jostled, subjecting the wafers to damage. In addition, and perhaps more importantly, the mere presence of people in close proximity to a wafer fabrication line can drastically affect the cleanliness of the operation, thus leading to the particulate contamination of the wafer surfaces. This situation cannot be corrected by any known air cleaning efforts.
Accordingly, the present invention provides a wafer cassette handling system wherein the movements of the cassette are accomplished automatically. This leads to greatly reduced particulate contamination levels and lessened opportunity for mechanical damage to the wafers contained in the cassette. Previous attempts at automating the process called for grabbing the cassette from the top which inherently leads to contamination.